After completion of the human genome project, the study of proteome (proteomics) has been widely practiced. The term “proteome” is used to describe the entire complement of proteins which are generated in a given biological organism or system based on translation. Examples of the proteomics include protein profiling and a similar study.
One of the most popular techniques adopted as the protein profiling is protein two-dimensional electrophoresis. Proteins have unique properties in electric charge and a molecular weight. Thus, in separating respective proteins from the proteome which is a mixture of a large number of proteins, it is possible to separate a larger number of proteins with high resolution by depending on both the electric charge and the molecular weight than depending on only the electric charge or only the molecular weight.
The two-dimensional electrophoresis includes two electrophoresis steps, i.e., (i) isoelectric focusing electrophoresis in which proteins are separated depending on electric charge and (ii) slabgel electrophoresis in which proteins are separated depending on a molecular weight (particularly, SDS-PAGE). Furthermore, the two-dimensional electrophoresis can be performed using a sample in the presence of or in the absence of denaturant. This is an excellent technique which allows several hundreds or more kinds of proteins to be separated at once (for example, see Patent Document 1 and Non Patent Document 1).
[Patent Document 1]
Japanese Laid-Open Patent Publication No. 30605/1999 (Tokukaihei 11-30605)(Publication date: Feb. 2, 1999)
[Non Patent Document 1]
“Electrophoresis Latest Protocol for More Quantitative Detection Analysis with Higher Sensitivity, Ranging from General Operation to Genomics And Proteomics!” (p 55-108: published by YODOSHA CO., LTD. in 2000)
The two-dimensional electrophoresis is performed as follows. A sample is subjected to isoelectric focusing electrophoresis in a first dimensional gel, and the first dimensional gel is retrieved and is applied to a second dimensional gel, and then separation in the second dimensional gel is performed on the basis of a molecular weight. Generally, the first dimensional gel in which the isoelectric focusing electrophoresis is performed is extremely thin compared with its width and length. Thus, it is difficult to discriminate front and rear faces and pH gradient directions of the gel. Furthermore, warpage and twist are likely to occur, so that it is difficult to keep its shape constant. This tends to cause low reproducibility of an electrophoresis result. Also, it is not easy to treat the first dimensional gel, so that it is difficult to enhance positional accuracy in moving the first dimensional gel to the second dimensional gel. In case of using SDS-PAGE to perform separation in the second dimensional gel, it is necessary to perform equilibration (SDS process and reduction: process with drug solution) in order to develop proteins of the first dimensional gel into the second dimension after finishing the electrophoresis in the first dimensional gel. The necessity to perform such a process with respect to the first dimensional gel causes uneven operations of different operators.
In this way, the two-dimensional electrophoresis is an excellent technique but requires a lot of skill. This technique depends on the skill of the operator, so that it is difficult to obtain quantitative data with high reproducibility by adopting the two-dimensional electrophoresis.
The present invention was made in view of the foregoing problems, and an object of the present invention is to enhance the convenience of the two-dimensional electrophoresis, to less depend on the operator's skill, and to enhance the reproducibility of the electrophoresis result. Specifically, an object of the present invention is to automate the two-dimensional electrophoresis.